Modified hydrolyzed vegetable protein microspheres and methods for preparation and use thereof

ABSTRACT

Modified hydrolyzed vegetable protein microspheres and methods for their preparation and use as oral delivery systems for pharmaceutical agents are described.

This is a division of application Ser. No. 08/051,739, filed Apr. 22,1993 and issued as U.S. Pat. No. 5,401,516 on Mar. 28, 1995; which inturn is a continuation-in-part of Ser. No. 07/995,508, filed Dec. 21,1992, now abandoned. This invention relates to modified hydrolyzedvegetable proteins and microspheres made from them. The microspheresreleasably encapsulate active agents and are suitable for oraladministration to mammals. Methods for the preparation of suchmicrospheres are also disclosed.

BACKGROUND OF THE INVENTION

The available means for delivering pharmaceutical and therapeutic agentsto mammals often are severely limited by chemical or physical barriersor both, which are imposed by the body. For example, oral delivery ofmany biologically-active agents would be the route of choice if not forthe presence of chemical and physicochemical barriers such as extreme pHin the gut, exposure to powerful digestive enzymes, and impermeabilityof gastrointestinal membranes to the active ingredient. Among thenumerous pharmacological agents which are known to be unsuitable fororal administration are biologicawny active peptides and proteins, suchas insulin. These agents are rapidly destroyed in the gut by acidhydrolysis and/or by proteolytic enzymes.

Much research has been devoted to developing effective oral drugdelivery methods and systems for these vulnerable pharmacologicalagents. The proposed solutions have included:

(a) co-administration of adjuvants (such as resorcinols and non-ionicsurfactants polyoxyethylene oleyl ether and n-hexadecyl polyethyleneether to increase the permeability of the intestinal walls; and

(b) co-administration of enzymatic inhibitors, such as pancreatictrypsin inhibitor, diisopropylfluorophosphate (DFF) and trasylol toavoid enzymatic degradation.

The use of such substances, in drug delivery systems, is limited howevereither because of their:

(a) inherent toxicity when employed in effective amounts; or

(b) failure to protect the active ingredient or promote its absorption;or

(c) adverse interaction with the drug.

Liposomes as drug delivery systems have also been described. Theyprovide a layer of lipid around the encapsulated pharmacological agent.The use of liposomes containing heparin is disclosed in U.S. Pat. No.4,239,754 and several studies have been directed to the use of liposomescontaining insulin; e.g., Patel et al. (1976) FEBS Letters Vol. 62, page60 and Hashimoto et al. (1979) Endocrinol. Japan, Vol. 26, page 337. Theuse of liposomes, however, is still in the development stage and thereare continuing problems, including:

(a) poor stability;

(b) inadequate shelf life;

(c) limited to low MW (<30,000) cargoes;

(d) difficulty in manufacturing;

(e) adverse interactions with cargoes.

More recently, artificial amino acid polymers or proteinoids, formingmicrospheres, have been described for encapsulating pharmaceuticals. Forexample, U.S. Pat. No. 4,925,673 (the '673 patent), the disclosure ofwhich is hereby incorporated by reference in its entirety, describessuch microsphere constructs as well as methods for their preparation anduse. The microspheres of the '673 patent are useful for encapsulating anumber of active agents, however there is a need in the art formicrosphere carriers that can encapsulate a broader range of activeagents such as lipophilic drugs.

Additionally, the method employed in the '673 patent for preparingproteinoids results in a complex mixture of high molecular weight (MW)(>1000 daltons) and low MW (≦1000 daltons) peptide-like polymers whichare difficult to separate. Moreover, small amounts of the low MWmicrosphere-forming proteinoids are obtained. Thus, an improved methodof preparing low molecular weight sphere-forming proteinoids is alsodesired.

SUMMARY OF THE INVENTION

The present invention relates to a modified hydrolyzed vegetable proteinmicrosphere and to a method for preparation of such microspheres. Theinvention provides stable microspheres which are preparable frominexpensive hydrolyzed vegetable protein, e.g. soybean protein, and asimple and economical method for making such microsphere. Microspheresmade according to the invention display improved stability andperformance in delivering biologically active materials to mammals.

According to the invention, modified hydrolyzed vegetable microspheresare prepared by dissolving hydrolyzed vegetable protein in an aqueousalkaline solution and adding a chemical modifier which reacts with freeamine residues present in the hydrolyzed protein. The pH of the reactionmixture is then lowered until the modified vegetable proteinprecipitates out from the mixture. The recovered protein readily formsmicrospheres and can be used to encapsulate various cargoes such aspharmaceutical agents. The microspheres are non-toxic and can be orallyor parenterally administered to mammals.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates levels of glucose detected in rat serum taken fromrats orally administered microsphere encapsulated insulin or raw(unencapsulated) insulin as described in Example 4.

FIG. 2 illustrates rat serum calcium levels after oral administration ofcalcitonin and calcitonin encapsulated in the vegetable proteinmicrosphere of the present invention as described in Example 5.

DETAILED DESCRIPTION OF THE INVENTION

All patents, patent applications, and literatures cited in thespecification are hereby incorporated by reference in their entirety. Inthe case of inconsistencies, the present disclosure, includingdefinitions, will prevail.

The modified vegetable protein microspheres of the present invention maybe prepared by reacting a hydrolyzed vegetable protein with a chemicalmodifying agent which reacts with free amino residues present in theprotein. The modified vegetable protein is then converted intomicrospheres which encapsulate active ingredients, e.g. drugs. A numberof advantages are obtainable by the present invention which include (a)the use of readily available and inexpensive starting materials and (b)a cost-effective method for preparing and isolatingmicrosphere-producing modified proteins. The overall modificationprocess is simple to perform and is amenable to industrial scale-upproduction.

According to the method of the present invention, an acid or enzymehydrolyzed vegetable protein is useful in practicing the invention. Thevegetable protein generally contains titratable carboxylic acid groups(COOH) ranging between about 3 and about 8 milliequivalents/g,preferably between about 4 and about 6 milliequivalents/g, total freeamino groups (NH₂) ranging between about 3 and about 9milliequivalents/g, preferably ranging between about 4 and about 7milliequivalents/g NH₂. The molecular weight of the vegetable proteinranges between about 100 D and about 2000 D, preferably between about200 and about 500 D.

Hydrolyzed vegetable protein is available from a variety of commercialsources. Non-limiting examples of such sources include Ajinomoto USA,Inc. (Teaneck, N.J. 07666, USA); Central Soya Co., Inc. (Fort Wayne,Ind., USA); and Champlain Industries, Inc. (Clifton, N.J., USA) andadditional companies listed in "Food Engineering Master", an annualpublication of Chilton Co., Radnor, Pa. 19089, USA. A particularlypreferred hydrolyzed vegetable protein in practicing this invention isavailable from Ajinomoto USA under the tradename AJI-EKI. This productis an acid hydrolyzed liquid soybean protein which is derived fromdefatted soybean meal.

If desired, a dried protein extract of the hydrolyzed vegetable proteinsolution may be used to prepare the modified vegetable protein of theinvention. The dried protein extract is preparable by extracting thehydrolyzed vegetable solution with a suitable solvent, e.g., methanol,followed by evaporating the solvent extract.

The vegetable protein is then dissolved in aqueous alkaline solution ofa metal hydroxide, e.g., sodium or potassium hydroxide, and heated at atemperature ranging between about 50° C. and about 70° C., preferablybetween about 50° C. and about 60° C., for a period ranging betweenabout 10 minutes and about 40 minutes, preferably about 15 minutes. Theamount of alkali employed per mmole of titratable NH₂ in the vegetableprotein generally ranges between about 2 and about 3 mmole, preferablybetween about 2.2 and about 2.5 mmole. The pH of the solution generallyranges between about 8 and about 13, preferably ranging between about 9and about 10.

Thereafter, an amine modifying agent is then added to the reactionmixture while stirring. The amine modifying agents are compositions thatcan react with the free amino (NH₂) residues present in the protein.Some non-limiting examples of amine modifying agents useful inpracticing the present invention include sulfonating agents such asbenzene sulfonyl chloride and acylating agents such as benzoyl chloride.

The amount of amine modifying agent in relation to the quantity ofhydrolyzed vegetable protein employed is based on the equivalents oftotal free NH₂ in the vegetable protein. Thus, between about 0.3 andabout 1.2 equivalents of modifying agent are used for each molarequivalent of total NH₂ groups in vegetable protein, and preferablybetween about 0.6 and about 1.0 equivalents of the modifying agent foreach molar equivalent of total NH₂ groups in the hydrolyzed vegetableprotein.

In practicing the invention, the mixture of vegetable protein andmodifying agent is maintained at a temperature generally ranging betweenabout 50° C. and about 70° C., preferably between about 60° C. and about65° C. for a period ranging between about 2 and about 5 hours.

The reaction is quenched by adjusting the pH of the mixture with asuitable acid, e.g., concentrated hydrochloric acid, until the pHreaches between about 2 and about 3. The mixture separates on standingat room temperature to form an opaque upper layer and a dark viscouslower layer. The upper layer is discarded and modified vegetable proteinis collected from the lower layer by filtration. The crude modifiedvegetable protein is then dissolved in water at a pH ranging betweenabout 9 and about 13, preferably between about 11 and about 13.Insoluble materials are removed by filtration and the filtrate is driedin vacuo. The yield of modified protein generally ranges between about30 and about 60%, usually about 45%.

The modified vegetable protein of the present invention is soluble inalkaline aqueous solution (pH≧9.0); partially soluble in ethanol,n-butanol and 1:1 (v/v) toluene/ethanol solution and insoluble inneutral water. The titratable functional groups remaining in thevegetable protein after modification are as follows: carboxylic acidgroups (COOH) ranging between about 1.5 and about 3.5milliequivalents/g, preferably about 2.3 milliequivalents/g, aminogroups (NH₂) ranging between about 0.3 and about 0.9 milliequivalents/g,preferably about 0.5 milliequivalents/g. The molecular weight of themodified vegetable protein ranges between about 200 D and about 2000 D,preferably between about 200 D and about 500 D.

The modified vegetable protein of the present invention can be usedimmediately to microencapsulate an active pharmacological agent or theprotein can be concentrated or dried by conventional means and storedfor future use.

The modified vegetable protein may be purified by fractionation on solidcolumn supports such as alumina, using methanol/n-propanol mixtures asthe mobile phase; reverse phase column supports using trifluoroaceticacid/acetonitrile mixtures as the mobile phase; and ion exchangechromatography using water as the mobile phase. When anion exchangechromatography is performed, a subsequent 0-500 mM sodium chloridegradient is employed. The modified vegetable protein may also bepurified by extraction with a lower alcohol such as methanol, butanol,or isopropanol to remove low molecular weight contaminants.

The following procedure may be employed to make microspheres frompurified modified vegetable protein. Modified vegetable protein isdissolved in deionized water at a concentration ranging between about 75and about 200 mg/ml, preferably about 100 mg/ml at a temperature betweenabout 25° C. and about 60° C., preferably about 40° C. Particulatematter remaining in the solution may be removed by conventional meanssuch as gravity filtration over filter paper.

Thereafter, the protein solution, maintained at a temperature of about40° C., is mixed 1:1 (V/V) with an aqueous acid solution (also at about40° C.) having an acid concentration ranging between about 0.05 N andabout 2 N, preferably about 1.7 N. The resulting mixture is furtherincubated at 40° C. for a period of time effective for microsphereformation as observed by light microscopy. In practicing this invention,the preferred order of addition is to add the protein solution to theaqueous acid solution.

Suitable acids include any acid which does not (a) adversely effect theprotein, e.g., chemical decomposition; (b) interfere with microsphereformation; (c) interfere with microsphere encapsulation of cargo; and(d) adversely interact with the cargo. Preferred acids for use in thisinvention include acetic acid, citric acid, hydrochloric acid,phosphoric acid, malic acid and maleic acid.

In practicing the invention, a microsphere stabilizing additivepreferably incorporated into the aqueous-acid solution or into theprotein solution, prior to the microsphere formation process. Thepresence of such additives promotes the stability and dispersibility ofthe microspheres in solution.

The additives may be employed at a concentration ranging between about0.1 and 5% (W/V), preferably about 0.5% (W/V). Suitable, butnon-limiting, examples of microsphere stabilizing additives include gumacacia, gelatin, polyethylene glycol, and polylysine.

Under these conditions, the modified vegetable protein molecules formhollow microspheres of less than 10 microns in diameter. If the proteinmicrospheres are formed in the presence of a soluble material, e.g., apharmaceutical agent in the aforementioned aqueous acid solution, thismaterial will be encapsulated in the hollows of the microspheres andconfined within the protein wall defined by the spherical structure. Inthis way, one can encapsulate pharmacologically active materials such aspeptides, proteins, and polysaccharides as well as charged organicmolecules, e.g., quinolones or antimicrobial agents, having poorbioavailability by the oral route. The amount of pharmaceutical agentwhich may be encapsulated by the microsphere is dependent on a number offactors which include the concentration of agent in the encapsulatingsolution, as well as the affinity of the cargo for the carrier.

The modified vegetable protein microspheres of the invention arepharmacologically harmless and do not alter the physiological andbiological properties of the active agent. Furthermore, theencapsulation process does not alter the pharmacological properties ofthe active agent. While any pharmacological agent can be encapsulatedwithin the protein microspheres, it is particularly valuable fordelivering chemical or biological agents which otherwise would bedestroyed or rendered less effective by conditions encountered withinthe body of the mammal to which it is administered, before themicrosphere reaches its target zone (i.e., the area in which thecontents of the microsphere are to be released) and which are poorlyabsorbed in the gastrointestinal tract.

The protein microspheres of the invention are particularly useful forthe oral administration of certain pharmacological agents, e.g., smallpeptide hormones, which, by themselves, pass slowly or not at allthrough the gastro-intestinal mucosa and/or are susceptible to chemicalcleavage by acids and enzymes in the gastrointestinal tract.Non-limiting examples of such agents include human or bovine growthhormone, interferon and interleukin-II, calcitonin erythropoietin,atrial naturetic factor, antigens and monoclonal antibodies.

The particle size of the microsphere plays an important role indetermining release of the active agent in the targeted area of thegastrointestinal tract. Microspheres having diameters between about ≦0.1microns and about 10 microns, preferably between about 5.0 microns andabout 0.1 microns, and encapsulating active agents are sufficientlysmall to effectively release the active agent at the targeted areawithin the gastrointestinal tract. Small microspheres can also beadministered parenterally by being suspended in an appropriate carrierfluid (e.g., isotonic saline) and injected into the circulatory systemor subcutaneously. The mode of administration selected will, of course,vary, depending upon the requirement of the active agent beingadministered. Large protein microspheres (>10 microns) tend to be lesseffective as oral delivery systems.

The size of the microspheres formed by contacting modified vegetableprotein with water or an aqueous solution containing active agents canbe controlled by manipulating a variety of physical or chemicalparameters, such as the pH, osmolarity or ionic strength of theencapsulating solution, and by the choice of acid used in theencapsulating process.

The vegetable protein-derived microspheres of the present invention aresuitable for oral administration of peptide hormones, e.g., insulin, andpolysaccharides, e.g., heparin, which otherwise would be quicklydestroyed in the stomach. They also are suitable for protecting thestomach from gastric irritants, such as aspirin and NSAID'S. When suchaspirin containing microspheres are orally administered, they passthrough the gastrointestinal mucosa and release the aspirin far morerapidly than conventional enterically coated aspirin, which first musttraverse the stomach and then must enter the bloodstream from theintestine after the enteric coating has dissolved.

The microspheres of the invention may be orally administered alone assolids in the form of tablets, pellets, capsules, and granulatessuitable for suspension in liquids such as water or edible oils.Similarly, the microspheres can be formulated into a compositioncontaining one or more physiologically compatible carriers orexcipients, and which can be administered via the oral route. Thesecompositions may contain conventional ingredients such as gelatin,polyvinylpyrrolidone and fillers such as starch and methyl cellulose.Alternatively, small microspheres (size less than 10 μm) can beadministered via the parenteral route.

The following examples are illustrative of the invention but are notintended to limit the scope of the invention.

EXAMPLE 1 Modification of Soybean Protein with Benzenesulfonyl Chloride

a. Extraction of soybean protein

3.2 L of acid hydrolyzed liquid soybean protein solution (AJI-EKI,Ajinomoto USA, Inc.) was reduced in vacuo to give 1440 g of solidpowder. This solid was extracted 3 times with methanol (2 L perextraction). Methanol was removed from the pooled extracts byevaporation. The yield of soybean protein as a dark brown powder was 608g. The functional groups of the soybean protein powder was titratedusing conventional procedures. See, for example, "A Laboratory Manual ofAnalytical Methods of Protein Chemistry," Vol. 1-3, Editors P. Alexanderand R. J. Block, Pergamon Press, 1960 and 1961. The soybean proteincontained the following functional groups: 3.7 milliequivalents/g ofCOOH; 0.44 milliequivalents/g free N-terminal NH₂ ; and 3.48milliequivalents/g total free NH₂. The molecular weight of the soybeanprotein ranged from 100 to 2000 D.

b. Modification of soybean protein

The dried soybean protein of step (a) (600 g, 2.5 equivalents of totalfree NH₂) was dissolved in 3 L of aqueous 2N potassium hydroxidesolution (2.25 mole excess) and the solution was heated at 60° C. for 30minutes. Thereafter, benzenesulfonyl chloride (460 g, 2.60 moles) wasadded dropwise to the mixture and the reaction temperature was monitoredso that it did not exceed 65° C. The reaction continued, with stirring,for 4 hours at 63° C. The reaction mixture cooled to room temperature,then acidified to pH 3.0 with 20% aqueous HCl solution and modifiedsoybean protein precipitated out. The modified soybean protein was thenwashed twice with distilled water (1 L) and dissolved in 2N aqueoussodium hydroxide solution until a pH of 8.5-9 resulted. The solution wasfiltered to remove particulates and the filtrate was reduced and driedin vacuo to give dry modified product (257 g, yield=24%). The producthad the following titratable groups: 2.3 milliequivalents/g of COOH; 0.2milliequivalents/g N-terminal free NH₂ ; and 0.3 milliequivalents/gtotal free NH₂.

EXAMPLE 2 Modification of Soybean Protein with Benzoyl Chloride

A commercial hydrolyzed water solution of soybean protein (AJI-EKI,Ajinomoto USA, Inc.) was used in this Example without furtherextraction. The protein in solution contained the following functionalgroups: 2.6 milliequivalents/ml of COOH and 2.0 milliequivalents/ml NH₂.The molecular weight of the soybean protein was approximately 6.5 kD.

To the soybean solution (240 mL, 0.5 equivalents free NH₂) was added 107mL of 10N aqueous potassium hydroxide solution followed by 200 mL ofdistilled water. The solution was then placed in an ice bath (5° C.) andbenzoyl chloride (70 g, 0.5 moles) was added dropwise within atemperature range between 10 to 25° C. The reaction mixture was thenstirred for 4.5 hours at room temperature. The pH of the reactionmixture was then reduced from 13.2 to 2.8 with concentrated HCl. Afterbeing allowed to settle for 1 hour, the precipitated modified soybeanprotein was collected by filtration and washed with distilled water. Thesoybean protein was then dissolved in 2N aqueous sodium hydroxidesolution to give a solution (pH 12.6) which was then evaporated toafford 48 g of dried product (% yield=41%).

EXAMPLE 3 Preparation of Empty Microspheres with Modified SoybeanProtein

This Example illustrates a method for the preparation and cleaning ofempty modified soybean protein microspheres.

PROCEDURE

1. Reagents:

a. Modified protein powder prepared as described in Example 1

b. Anhydrous citric acid (USP)

c. Gum acacia NF

d. Deionized water

e. Glacial acetic acid

2. Equipment

a. pH meter

b. Eppendorf pipette (0-100 ul) and tips

c. Water bath, 40° C.

d. liquid nitrogen

e. lyophilization flasks

3. Preparation of Solutions:

a. Protein solution--Dissolve 100 mg modified soybean protein in 1 mldeionized water (or multiples thereof). Filter through a Whatman #1filter paper (if necessary) and keep at 40° C. in a water bath. This issolution A.

b. 1.7 N citric acid with 0.5% acacia--Dissolve 5 g of acacia and 109 gof citric acid in 1 liter deionized water. Incubate at 40° C. This issolution B.

4. Preparation of Microspheres:

a. Add all of solution A to solution B rapidly in one step whileswirling solution B by hand, in a 40° C. water bath.

EXAMPLE 4 Preparation of Soybean Protein Microsphere ContainingEncapsulated Heparin

This Example describes a method for the preparation and cleaning ofheparin microspheres.

PROCEDURE

1. Reagents:

a. Modified protein powder prepared as described in Example 1

b. Heparin

c. Anhydrous citric acid (USP)

d. Gum acacia NF

e. Deionized water

f. Desiccant

g. Liquid nitrogen

2. Equipment:

a. Magnetic stirrer

b. Buret

c. Microscope

d. Clinical centrifuge

e. Dialysis membrane tubing (Spectrum 6, 10 mm, 50,000 M.W. Cutoff)

f. pH meter

g. Lyophilizer (Labconco #75035)

h. Lyophilizing flasks (150-300 mL)

i. Rotating shell freezer

j. Isopropanol/dry ice bath or liquid N₂

k. Mortar and pestle

l. Storage containers (500 mL)

m. Eppendorf pipet (0-100 uL)

n. Plastic closures for dialysis tubing (Spectrum)

o. 2 mL syringe with 0.45 μm Acrodisk

3. Preparation of Solutions:

a. Protein Solution A* (80 mg/ml):

Add 160 mg of modified soybean protein and dissolve to 1 ml withdeionized water. Using a 2 ml syringe filter through a 0.45 μm Acrodiskinto a 10 ml test tube. Keep at 40° C.

b. Solution B (1.7 N citric acid with 1% gum):

Dissolve 10 g of acacia and 109 g of citric acid in 1 liter deionizedwater.

c. Solution C (Heparin solution):

Dissolve heparin in Solution B at 150 mg/mL and keep at 40° C.

4. Preparation of Microspheres:

a. Add all of solution A to solution C quickly while swirling solution Cslowly, by hand, in a 40° C. water bath.

5. Cleaning of Microspheres:

a. Transfer the suspension with a syringe (no needle) to dialysis tubingand seal with plastic closures. Tubing should be no more than 70% full.

b. Discard any amorphous material sedimented and/or aggregated on thesurface.

c. Dialyze the microsphere suspension against acetic acid (using 20 mLof acetic acid solution per ml of microsphere suspension) while stirringthe acetic acid solution with a magnetic stirrer.

d. Replace the acetic acid solution every hour. Continue dialyzing for atotal of 3 hours.

6. Lyophilization:

a. Add one part of 50% Trehalose (Sigma) into nine parts of dialyzedmicrosphere solution. Flash freeze microspheres in a freeze-drying flaskusing the shell freezer adjusted to rotate at ca. 190 rpm and immersedin a liquid nitrogen bath.

b. Freeze dry for 24 hours or until dry as evidenced by lack ofself-cooling.

c. Record weight of dry microspheres.

d. Grind to a fine powder with mortar and pestle.

e. Transfer to amber container, seal with desiccant, and store at roomtemperature.

7. Resuspension:

a. Weigh the lyophilized powder and calculate the amount of protein inthe powder.

b. Add 0.85 N citric acid into the lyophilized powder at 40° C. Thefinal concentration of protein is 80 mg/ml.

EXAMPLE 5 Evaluation of Insulin Microspheres in Rats

In this Example, the insulin microspheres prepared in accordance withExample 3 were evaluated in rats. Twelve rats were divided into twogroups as follows:

1. oral insulin microspheres: 3 mg insulin/kg body weight by oral gavage(six rats);

2. Raw insulin (no encapsulation): 3 mg insulin/kg body weight by oralgavage (six rats).

Oral gavage dosing of rats was performed. Insulin microspheres wereprepared immediately prior to dosing and Group 1 rats each receive anappropriate dosage of the microsphere suspension. Group 2 rats receivedthe unencapsulated insulin. Approximately 0.5 ml of blood was withdrawnfrom each rat just prior to dosing ("0" time) and 1 to 6 h post-dosing.Serum from the blood samples were stored at -20° C.

The glucose levels of thawed serum taken from the rats were analyzed byconventional methods. As shown in FIG. 1, sharp decreases in serumglucose levels were observed in groups 1 rats receiving the encapsulatedinsulin. In contrast, the serum glucose levels in group 2 rats slightlyincreased from t=0. The results show that encapsulated insulin had agreater biological effect, when administered orally, in contrast tounencapsulated insulin.

EXAMPLE 6 Preparation of Microsphere Encapsulated Calcitonin

Encapsulation of salmon calcitonin in soybean protein microspheres wereperformed in the same manner described in Example 3. Calcitonin wasobtained from Sandoz (Basil, Switzerland) and a 150 mg/mL calcitoninsolution in 1.7 N citric acid solution with 1% gum was prepared asdescribed in Example 3.

EXAMPLE 7 Evaluation of Calcitonin Microspheres in Rats

In this Example, the calcitonin microspheres prepared in accordance withExample 5 were evaluated in rats. Twelve rats were divided into twogroups as follows:

1. oral calcitonin microspheres: 60 μg calcitonin/kg body weight by oralgavage (six rats).

2. oral unencapsulated microspheres: 60 μg calcitonin/kg body weight byoral gavage (3 rats) (Control).

Oral gavage dosing of rats was performed. Calcitonin microspheres wereprepared immediately prior to dosing and Group 1 rats received anappropriate dosage of the microsphere suspension. Group 2 rats receivedthe unencapsulated calcitonin. Approximately 0.5 ml of blood waswithdrawn from each rat just prior to dosing ("10" time) and 1 h, 2 hand 3 h post-dosing. Serum from the blood samples were stored at -20° C.

The calcium levels of thawed serum taken from group 1 and 2 rats wereanalyzed by conventional methods. As shown in FIG. 2, sharp decreases inserum calcium levels were observed in group 1 rats receiving theencapsulated calcitonin. In contrast, the calcium levels in group 2 ratsslightly decreased from t=0. The results show that encapsulatedcalcitonin had a greater biological effect, when administered orally, incontrast to unencapsulated calcitonin.

What is claimed is:
 1. A microsphere comprising(a) a hydrolyzedvegetable protein modified with a monofunctional amine reactivemodifying agent; and (b) a biologically active agent;wherein saidmicrosphere is hollow and said biologically active agent is encapsulatedtherein.
 2. A microsphere according to claim 1, wherein said aminereactive modifying agent is selected from the group consisting ofbenzene sulfonyl chloride and benzoyl chloride.
 3. A microsphereaccording to claim 1, wherein said biologically-active agent is selectedfrom the group consisting of a protein, a polysaccharide, an antigen, amonoclonal antibody, insulin, calcitonin, and erythropoietin.
 4. Amicrosphere according to claim 1, wherein said biologically-active agentcomprises a protein.
 5. A microsphere according to claim 4, wherein saidprotein comprises insulin.
 6. A microsphere according to claim 4,wherein said protein comprises human growth hormone.
 7. A microsphereaccording to claim 4, wherein said protein comprises bovine growthhormone.
 8. A microsphere according to claim 4, wherein said proteincomprises interferon.
 9. A microsphere according to claim 4, whereinsaid protein comprises interleukin II.
 10. A microsphere according toclaim 4, wherein said protein comprises atrial naturetic factor.
 11. Amicrosphere according to claim 4, wherein said protein comprisescalcitonin.
 12. A microsphere according to claim 1, wherein saidbiologically active agent comprises a polysaccharide.
 13. A microsphereaccording to claim 12, wherein said polysaccharide comprises heparin.14. A microsphere according to claim 1, wherein said biologically activeagent comprises an antigen.
 15. A microsphere according to claim 1,wherein said biologically active agent comprises a monoclonal antibody.16. A microsphere according to claim 1, wherein said biologically activeagent comprises aspirin.
 17. A microsphere according to claim 1, whereinsaid biologically active agent comprises erythropoietin.
 18. Amicrosphere according to claim 1, where in said biologically activeagent comprises a nonsteroidal anti-inflammatory drug.
 19. A microsphereaccording to claim 1, wherein said biologically active agent comprisesan antimicrobial agent.
 20. A microsphere according to claim 1, whereinsaid biologically active agent comprises quinolone.